QuakeIndex

Earthquake · reviewed by a seismologist

M 3.4ml

Earthquake near Unalaska, AK

No earthquake was likely felt in Unalaska in the 24 hours to 1:27 am AKST (10:27 UTC). The last one was M 4.4, 117 km (72 mi) ESE, at 3:00 pm AKST on 11 November 2026, estimated intensity II (weak) in town. Every earthquake near Unalaska

This page: a magnitude 3.4 earthquake was recorded 16 km (10 mi) west-southwest of Unalaska, AK, at 7:21 pm AKDT on 18 July 2020 (03:21 UTC), 10 km deep. 1 person has reported feeling it to USGS.

USGS: 16 km WSW of Unalaska, Alaska

7:21 pm AKDT, Jul 18, 2020 · · 10 km deep · released about 1.9 tons of TNT

Every earthquake near Unalaska Felt it? Tell USGS Check my area
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Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
7:21 pm AKDT on 18 July 2020 ()
Where
16 km (10 mi) west-southwest of Unalaska, AK · earthquakes near Unalaska
Magnitude
M 3.4 (ml)
Depth
10 km below the surface
Felt
1 report · strongest reported intensity III
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2240 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 57 km (35 mi) from the epicentre. In Unalaska, 16 km away, the estimate is intensity III (weak). Estimated from magnitude, depth and distance with the intensity equation USGS Did You Feel It? uses; felt reports, where there are any, are the measurement.

Likely felt in: Unalaska 16 km, intensity III. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 1.9 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.4 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 89,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 4,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 2,800× the energy of this one
  4. This earthquake M 3.4 about 1.9 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 4× more

Energy from the Gutenberg–Richter relation (log10E = 1.5M + 4.8), rounded to two figures; bar length is magnitude, which is already a logarithm of energy. Magnitudes of past earthquakes from the USGS catalogue.

For this area

The largest earthquake within 50 km since 2016 was M 4.8 on 2020-03-30 — about 130 times the energy of this one.

Before 2016, the USGS record lists 16 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.2 36 km ESE of Unalaska, Alaska · 47 km ESE of this epicentre
  2. 6.1 56 km SSW of Unalaska, Alaska · 46 km S of this epicentre
  3. 6.0 51 km SW of Unalaska, Alaska · 36 km SW of this epicentre
  4. 6.0 64 km SW of Unalaska, Alaska · 48 km SW of this epicentre
  5. 5.9 27 km WNW of Dutch Harbor, Alaska · 23 km NNW of this epicentre

Since 2016: the QuakeIndex catalogue (US, M1.5+), built from the USGS FDSN event service. Before 2016: USGS ComCat, M5+ from 1900. Distances are between epicentres. This is the record, not a forecast.

Where

Epicentre 53.8051, -166.7523. Map © OpenStreetMap contributors.

Aftershocks so far

55 earthquakes have been recorded within 50 km since this one.

  1. 2.1 48 km SSW of Unalaska, AK
  2. 1.7 50 km SW of Unalaska, Alaska
  3. 1.6 58 km SW of Unalaska, Alaska
  4. 2.3 Fox Islands, Aleutian Islands, Alaska
  5. 1.6 38 km S of Unalaska, Alaska
  6. 1.8 27 km WSW of Unalaska, Alaska
  7. 2.6 60 km SW of Unalaska, Alaska
  8. 2.6 58 km SW of Unalaska, Alaska
  9. 2.1 37 km W of Dutch Harbor, Alaska
  10. 1.6 14 km WSW of Dutch Harbor, Alaska
  11. 2.6 13 km WSW of Unalaska, Alaska
  12. 2.0 55 km SSW of Unalaska, Alaska
  13. 2.0 24 km ESE of Unalaska, Alaska
  14. 1.8 11 km W of Dutch Harbor, Alaska
  15. 1.6 13 km NE of Dutch Harbor, Alaska

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of . QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.